1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image in an electronic photographing process using a laser printer, etc.
2. Description of the Related Art
In most image forming apparatuses, an image is transferred onto a paper sheet by passing the sheet through an image transfer unit of an electronic photographic process unit in which such steps as charging, exposure, development, transfer, peeling, cleaning, etc. are carried out.
The paper sheet bearing the image is passed between a pair of fixing rollers, so that the image is fixed.
This type of conventional image forming apparatus (e.g. laser printer) employs a disposable cartridge type developer ("toner") supply device for supplying toner to a developing unit built in the apparatus body.
The toner supply cartridge ("supply container") is mounted exchangeably in the developing unit in the apparatus body.
Non-transferred toner, which has not been transferred on the paper sheet in the image transfer unit, is removed from a photosensitive body by a cleaning device. The removed toner is brought to the outside of the process unit and is recovered in the disposable cartridge type container. The toner recovering cartridge ("recovery container"), too, is mounted exchangeably in the process unit built in the apparatus body.
The "empty" state of the supply cartridge and the "full" state of the recovery cartridge are detected by a detector, and the operator exchanges the cartridges, when necessary, on the basis of the detection result.
In the prior art, the toner supply cartridge and the toner recovery cartridge are separated, or, in order to simplify the exchange process, the toner supply cartridge and the toner recovery cartridge are integrated, respectively, with the developing means, cleaning means, photosensitive drum, etc.
However, if the toner supply cartridge and the toner recovery cartridge are separated, the cartridges must be exchanged each time the toner is supplied or non-used toner is dumped. This is troublesome.
On the other hand, when the toner supply cartridge and the toner recovery cartridge ar integrated with the developing means, cleaning means or photosensitive drum, the exchange process is simplified; however, the storage amounts of supply toner and non-used toner are limited owing to the practical size of the integrated cartridge unit. Consequently, the exchange cycle of the entire unit is shortened, and the unit must be exchanged earlier than the end of lifetime of the relatively expensive developing means, cleaning means and photosensitive drum. Thus, the running cost of the apparatus increases.